James Woods guest stars as a Dr. Nate Lennox, a former professor of biochemistry who was Abby's early medical school mentor. Lennox, suffering from advanced ALS and now able to move only his eyes, is admitted with pneumonia. The progression of his disease is shown in reverse through a series of flashbacks. As Ray, Sam and Luka begin limited treatment under the proxy of his attendant, Abby believes Lennox has communicated different wishes, leading to a struggle to determine what course of action should be taken, and how long to fight the inevitable.